diff --git a/src/server/__tests__/conversation-service.test.ts b/src/server/__tests__/conversation-service.test.ts
index dc678359..9e812b76 100644
--- a/src/server/__tests__/conversation-service.test.ts
+++ b/src/server/__tests__/conversation-service.test.ts
@@ -165,6 +165,32 @@ describe('ConversationService', () => {
     expect(env.CLAUDE_CODE_ENTRYPOINT).toBeUndefined()
   })
 
+  test('buildChildEnv uses the session-selected model for session-scoped providers', async () => {
+    const providerService = new ProviderService()
+    const provider = await providerService.addProvider({
+      presetId: 'custom',
+      name: 'Switchable',
+      apiKey: 'provider-key',
+      baseUrl: 'https://api.switchable.example',
+      apiFormat: 'openai_chat',
+      models: {
+        main: 'old-provider-main',
+        haiku: 'new-provider-haiku',
+        sonnet: 'new-provider-sonnet',
+        opus: 'new-provider-opus',
+      },
+    })
+
+    const service = new ConversationService() as any
+    const env = (await service.buildChildEnv('/tmp', undefined, {
+      providerId: provider.id,
+      model: 'new-provider-sonnet',
+    })) as Record<string, string>
+
+    expect(env.ANTHROPIC_BASE_URL).toBe(`http://127.0.0.1:3456/proxy/providers/${provider.id}`)
+    expect(env.ANTHROPIC_MODEL).toBe('new-provider-sonnet')
+  })
+
   test('buildChildEnv can force official auth even when a custom default provider exists', async () => {
     const ccHahaDir = path.join(tmpDir, 'cc-haha')
     await fs.mkdir(ccHahaDir, { recursive: true })
diff --git a/src/server/services/conversationService.ts b/src/server/services/conversationService.ts
index 08e2d807..0db3170d 100644
--- a/src/server/services/conversationService.ts
+++ b/src/server/services/conversationService.ts
@@ -556,6 +556,9 @@ export class ConversationService {
       typeof options?.providerId === 'string'
         ? await this.providerService.getProviderRuntimeEnv(options.providerId)
         : null
+    if (explicitProviderEnv && options?.model?.trim()) {
+      explicitProviderEnv.ANTHROPIC_MODEL = options.model.trim()
+    }
 
     return {
       ...cleanEnv,